1. Field of the Invention
This invention generally relates to an ink-jet printer and more in particular to an ink-jet nozzle for use in an ink-jet printer and a method for manufacturing such a nozzle.
2. Description of the Prior Art
An ink-jet printer is well known in the art. It is a non-impact type printer which includes an ink-jet nozzle from which ink droplets are discharged under electrostatic acceleration to be impinged upon a recording medium after suitable deflection in a dot-matrix format to form characters on the recording medium. In an ink-jet printer, a nozzle for discharging ink droplets plays an important role in the ink-jet printing characteristics. For example, it must be hard enough to prevent formation of cracks or scratches on the nozzle passage through which ink is discharged. At the same time, it should not be too hard to present difficulty in its manufacturing process.
According to one well-known method for manufacturing an ink-jet nozzle, nickel is electrodeposited onto a wire, the diameter of which corresponds to the diameter of a desired nozzle, to form a nickel rod enclosing the wire at its center. Then the thus formed nickel rod is sliced into a disc of approximately 0.5 mm thick. Upon polishing both sides of the sliced disc, the wire at the center is removed with the use of an appropriate chemical agent thereby forming a desired nozzle for use in an ink-jet printer.
As a modification of the above-described method, it is also known to manufacture a nozzle having Hv (Vickers hardness) of 300-350 at the inner periphery which gradually changes to 200-250 at the outer periphery, as shown in FIG. 1, by changing electrodeposition conditions, particularly the cathode current density, with the use of total nickel chloride solution. Moreover, it is also known that nickel sulfamate solution may be substituted for total nickel chloride. It is also known to manufacture the nozzle having Hv of 400-600 at its inner and outer peripheries by adding nickel chloride or a stress reducing agent such as a brightener, saccharin, etc. to nickel sulfamate solution.
In accordance with the above-described prior art with the use of total nickel chloride solution or nickel sulfamate solution, a difference in hardness between the inner and outer portions of the nozzle member is produced by controlling the cathode current density inside the electrolytic solution of the same composition. Therefore the initial rate of electrodeposition is extremely slow since electrodeposition is carried out with a low current density. Moreover, to increase the hardness just by controlling the current density is rather limited.
It is also to be noted that the hardness Hv in the range between 300 and 350 is not enough and chips are formed during the process of manufacturing the nozzle, which chips remain as flashes after removal of the wire. Therefore, a step for removing flashes is required. Moreover, during maintenance operation, such as washing and cleaning, of the nozzle head, scratches tend to be formed at the edge portion of the nozzle mouth from which ink is discharged, thereby adversely affecting the ink discharging characteristics. Thus, this prior art nozzle is disadvantageous because its scratch-resistance property is unsatisfactory.
It is true that the prior art also provides an ink-jet printer nozzle having the Hv hardness in the range between 400 and 600. However, this prior art nozzle has such high values of Hv throughout its body including the outer peripheral portion which has nothing to do with the ink discharging characteristics. Thus, it is also disadvantageous because machining such as cutting (slicing) and shaping requires a long period of time and wear of machine tools is extremely severe.